Field of the Invention
The present invention relates to Trichoderma mutant strains deficient in the production of secondary metabolites, methods of obtaining the Trichoderma mutant strains, and methods of producing heterologous polypeptides in the Trichoderma mutant strains.
Description of the Related Art
Trichoderma has been shown to be useful as a host cell for the recombinant production of polypeptides having biological activity (WO 96/00787 and WO 97/26330). Trichoderma hosts with the desirable traits of increased protein expression and secretion may not necessarily have the most desirable characteristics for successful fermentation. The fermentation may not be optimal because of the production of biological substances detrimental to the production, recovery, or application of a particular polypeptide of interest.
Peptaibols are synthesized by large multidomain enzymes known as non-ribosomal peptide synthetases that assemble compounds from a range of precursors (including nonproteinogenic amino acids and hydroxy or carboxyl acids), which can be N-methylated, acylated, reduced, or epimerized (Marahiel et al., 1997, Chem. Rev. 97: 2651-2674; Zocher and Keller, 1997, Adv. Microb. Physiol. 38: 85-131). The synthetases have a modular structure in which each module is a semiautonomous unit that recognizes, activates, and modifies a single residue of the final peptide. Each module can be further partitioned into distinct adenylation, thiolation, and condensation domains, which together represent a minimal repeating unit of such a synthetase (Stein et al., 1996, Journal of Biological Chemistry 271: 15428-15435).
Mukherjee et al., 2012, Microbiology 158: 35-45, describe secondary metabolism in Trichoderma. Mukherjee et al., 2011, Journal of Biological Chemistry 286: 4544-4554, disclose two classes of new peptaibols synthesized by a single non-ribosomal peptide synthetase of Trichoderma virens. Kubicek et al., 2011, Genome Biology 12: R40, describe a comparative genome sequence analysis underscoring mycoparasitism as the ancestral life style of Trichoderma. Neohof et al., 2007, Microbiology 153: 3417-3437, describe intact-cell MALDI-TOF mass spectrometry analysis of peptaibol formation by the genus Trichoderma. 
Mukherjee et al., 2012, supra, also describe that several Trichoderma spp. strains produce terpenoids synthesized from five-carbon isopentenyl units by the action of terpene cyclases. The T. virens genome harbors six terpene cyclases, while T. atroviride and T. reesei have three each.
The present invention relates to improved Trichoderma hosts that combine the capacity for expression of commercial quantities of a polypeptide of interest while being deficient in the production of peptaibol(s) and terpene(s) that can complicate production, recovery, or application of the polypeptide.